1. Field of the Invention
This invention relates to a fluidity controlling agent for paints which gives thixotoropic properties to a coating film when it is applied to the paint and hardly produces sagging even in the formation of thick coating film, and more particularly to a fluidity controlling agent useful for heat curing paints.
2. Related Art Statement
Heretofore, calcium carbonate, organic bentonite, hydrophobic silcia, organic polyamide wax, polyethylene wax and the like have been used as fluidity controlling agents for paints. Recently, compounds having a urea bond have been included in the above known fluidity controlling agents. For example, Japanese Patent laid open No. 49-99,131 discloses a fluidity controlling agent consisting of a urea adduct obtained by reacting (a) a diisocyanate compound, (b) primary and/or secondary polyamine and, if necessary, (c) monofunctional alcohol, oxime, amine and/or alkanol amine at such a ratio that the amount of primary and/or secondary amino group does not stoichiometrically exceed the amount of isocyanate group.
Furthermore, U.S. Pat. No. 4,311,622 discloses a fluidity controlling agent consisting of a reaction product of a diisocyanate and a monoamine or hydroxymonoamine of an aliphatic hydrocarbon having a carbon number of 1-5.
The fluidity controlling agent having such a urea bond has an advantage in that the effect of preventing sagging is large even in paints containing a large amount of a high polarity solvent such as alcohol, ketone or the like because the intermolecular force of the urea bond is generally strong, and the effect of preventing sagging is hardly lost even when the temperature is increased during curing when it is applied to heat curing paint. However, when such a fluidity controlling agent as disclosed in Japanese Patent laid open No. 49-99,131 is applied to a transparent clear paint containing no pigment, the sagging prevention effect is lowered with passage of time, and the gloss of the coating film is undesirably degraded if the curing is performed at a temperature below 140.degree. C. even after the production of the paint.
On the other hand, the fluidity controlling agent made from monoamine or hydroxymonoamine of aliphatic hydrocarbon having a carbon number of 1-5 and diisocyanate, for example, benzylamine and hexametylene diisocyanate as disclosed in U.S. Pat. No. 4,311,622 is high at the melting point of the coating film and has a drawback in that when it is applied to a transparent clear paint containing no pigment, if the curing temperature is lower than 140.degree. C. (a typical baking temperature), the gloss of the coating film is degraded.
Under the above circumstances, the inventors have made studies with respect to a means for solving the above problems and found that very high thixotropic properties are obtained by using as a fluidity controlling agent product a reaction between a primary monoamine having an amino group directly bonded to an aromatic ring and aliphatic diisocyanate. The present inventors consequently proposed a fluidity controlling agent containing a component obtained by reacting aniline and aliphatic diisocyanate and a component obtained by reacting oxygen-containing primary monoamine and aliphatic diisocyanate at a particular mixing ratio (Japanese Patent laid open No. 61-97,375). In this case, however, the oxygen-containing primary monoamine is used, so that when the molecular weight of a resin used as an organic binder is small, the water resistance of the coating film undesirably lowers.